A good way to get the air out of a ZipLoc is to insert an ordinary drinking straw at one end of the top; close the lock as far as the straw; suck the air out; and then, as quickly as you can, pull out the straw and zip the last fraction of an inch. Then, there really is very little air in there.
Like Tom, I'd freeze 'em without the canisters (less air per film with the ZipLoc), though unlike Tom, I'd put 'em back in the canisters to carry 'em when they're thawed.
Cheers,
R.